1. Field of the Invention
The invention relates to an exhaust gas recirculation system for a combustion engine with an exhaust gas inlet, an exhaust gas outlet, and an exhaust gas cooling device that features a heat exchanger unit through which a coolant flows, as well as with a bypass channel via which the heat exchanger unit can be bypassed and in which a bypass flap is arranged.
2. Background Art
In the known exhaust gas recirculation systems, the exhaust gas is conducted from the exhaust manifold back to the induction pipe of the combustion engine via an exhaust gas recirculation channel. The exhaust gas flow is regulated thereby by an exhaust gas recirculation valve arranged in the exhaust gas recirculation channel.
Moreover it is known to arrange cooling devices in the exhaust gas recirculation channels so that the exhaust gas is fed back into the induction pipe cooled, as a result of which the NOx emissions can be reduced. However, since the fastest possible heating of the coolant and also of a catalyst is desired when the engine is started, exhaust gas recirculation systems were embodied in which the exhaust gas cooling device can be bypassed via a bypass channel, whereby the bypass channel is governed by a bypass flap or a bypass valve.
In DE 198 41 927 A1, a device is described for recirculating an exhaust gas flow to the induction pipe of a combustion engine, in which the exhaust gas cooling device is embodied with the bypass channel as a unit in which the bypass flap is arranged between an exhaust gas inlet and an exhaust gas outlet of the cooling device, so that the path through the cooler can be bypassed via the bypass channel. The exhaust gas recirculation valve regulating the amount of exhaust gas is arranged in the subsequent region of the exhaust gas recirculation channel. By embodying the cooler with the bypass channel as a unit, a compact construction with a reduction in construction space and weight resulting therefrom is to be achieved.
In EP 0 916 837 B 1 a device for the exhaust gas recirculation for a combustion engine is described in which the exhaust gas cooling device and the exhaust gas recirculation valve are embodied as a unit, whereby a control element of the valve is cooled at the same time by the flowing coolant. This is intended to result in a reduction of the thermal load of the control element. Bypassing the exhaust gas cooler via a bypass channel is not provided for.
In DE 197 40 998 A1 an exhaust gas recirculation system for a combustion engine is described in which an exhaust gas recirculation valve is mounted on a connection base that is in turn mounted on a cooling device arranged on the induction pipe. The thermal load of the inlet manifold is to be reduced by such a design. However, based on the design the cooling device present here serves primarily for the thermal uncoupling of the induction pipe from the exhaust gas recirculation valve, whereby an adequate cooling of the exhaust gas to reduce the NOx emission is not provided for.